The use of barium aluminate material in the electron emission means of discharge electric lamps is disclosed in U.S. Pat. Nos. 2,871,196 and 2,957,231, both of which patents being assigned to the assignee of the present invention. As therein disclosed, said electron emissive material can be dispersed in the pores of a sintered refractory metal such as a sintered tungsten pellet by impregnation for use as an electrode member in a photographic flash tube type gaseous electric discharge lamp. The breakdown or starting voltage of said barium aluminate electron emissive material is said to exceed 250 volts depending upon the particular type lamp construction, and higher voltage operation is also said to be possible with the disclosed electron emission means. Use of barium tungstate compounds as emission material having similar voltage operating characteristics in sodium vapor type discharge lamps is disclosed in U.S. Pat. No. 3,708,710, also assigned to the present assignee. The described lamps further include a filling of sodium along with a rare gas such as xenon to facilitate starting along with mercury for improved efficiency. The particular electron emissive material therein disclosed is said to be a good emitter and at the same time more resistant to vaporization in ion bombardment when used in this type lamp than emission materials previously available.
While both of the foregoing barium aluminate and barium tungstate emission materials exhibit long term stability of operation during lamp life, it would be understandably beneficial from an energy efficiency and cost standpoint to operate at lower voltage requirements. Thus, lower breakdown voltage and operating voltage characteristics for the electron emission means of an electric discharge lamp represents a desirable improvement especially if these lower voltage requirements can be obtained without sacrificing other desirable characteristics during lamp operation.